This invention is in the field of gear actuation mechanisms for automatic transmissions. The invention is particularly suited for gear actuation of dual clutch automatic transmissions.
In a dual clutch automatic transmission, it is necessary to select at most one even gear and at most one odd gear at any particular time. For maximum operational flexibility, it is desirable for the choices of odd gear and even gear to be independent. Typically, this is accomplished by providing two independent gear actuation mechanisms, including two motors. The motors and associated circuitry account for a substantial fraction of the costs of the actuation systems. Therefore, it is desirable to have one motor rather than two.
A well know actuation system uses a single motor to turn a single drum which actuates both even and odd gears. However, that system does not allow even and odd gears to be selected independently. For example, when sixth gear is selected, the only odd gears available would be fifth or seventh. Third gear cannot be selected, so a direct shift from sixth gear to third gear is impossible.
This invention uses a planetary gear set to multiplex a single motor, such that the motor is alternately connected to one of two independent drums. One drum actuates the odd gears and the other actuates the even gears. Although only one drum may be moved at a time, all positions on each drum are available independent of the position of the other drum.
Furthermore, the invention takes advantage of the relationship between the clutch state and the need to change gears to determine which of the two drums should be driven by the motor. Specifically, the odd gear is never changed while driving in an odd gear and the even gear is never changed while driving in an even gear. Therefore, the motor drives the even drum whenever the odd clutch is engaged and drives the odd drum whenever the even clutch is engaged.